Master Linux System Management: Root, Users, Groups, and Permission Controls

Linux System Management: Deep Dive into Root User, Users & Groups, Permission Controls, and File Permission Changes

Introduction

In the previous article we explored file operation commands such as cp, mv, rm, and text‑processing tools like grep, wc and pipelines. This article continues the core concepts of Linux system management, including the role of the root user, user and group management, viewing permission information, and the use of chmod and chown commands.

1. The root user

In Linux, the root user (also called the superuser or administrator) has all permissions on the system and can perform any operation, such as installing software, modifying system files, and managing user accounts.

1.1 Switch to the root user

You can switch to the root account with the su command: su After entering the root password you obtain full root privileges.

1.2 Use sudo instead of switching

Modern distributions recommend using sudo to run commands that require root privileges, rather than logging in as root directly.

sudo apt-get update  # execute a command that needs root rights

1.3 The sudoers file

The configuration for sudo is stored in /etc/sudoers, which defines which users and groups may execute which commands.

2. Users and groups

Linux is a multi‑user operating system; managing users and groups is essential for system security and permission control.

2.1 User management

Add a new user: sudo adduser username Delete a user: sudo deluser username Change a user's password:

sudo passwd username

2.2 Group management

Add a group: sudo groupadd groupname Delete a group: sudo groupdel groupname Add a user to a group:

sudo usermod -a -G groupname username

3. Viewing permission information

Each file and directory has permission settings that control who can read, write, or execute it.

3.1 View file permissions

Use ls -l to display permissions: ls -l filename Example output:

-rwxr-xr-- 1 owner group 4096 Dec 20 12:34 filename

Here -rwxr-xr-- means the owner has read, write, and execute permissions, while the group and others have read and execute only.

3.2 Composition of file permissions

r

: read permission w: write permission x: execute permission

4. chmod command: Changing file permissions

The chmod command modifies the permissions of files and directories.

4.1 Numeric mode

chmod 755 filename

In this example, 7 (rwx) gives the owner full permissions, 5 (r-x) gives the group read and execute, and the final 5 gives others the same.

4.2 Symbolic mode

chmod u+x filename

This adds execute permission for the file owner.

5. chown command: Changing file owner and group

The chown command changes the owner and group of files or directories.

5.1 Change file owner

sudo chown newowner filename

5.2 Change file owner and group

sudo chown newowner:newgroup filename

Conclusion

This article explored the core concepts of Linux system management, including the role and privileges of the root user, how to manage users and groups, how to view permission information, and the practical use of chmod and chown commands. Mastering these topics is essential for anyone seeking deep understanding of Linux administration.